Exhaust constituent sensors have been used for many years in automotive vehicles to sense the presence of constituents in exhaust gasses (e.g., oxygen, hydrocarbons, nitrous oxides) and to sense, for example, when an exhaust gas content switches from rich to lean or lean to rich. One known type of exhaust constituent sensor includes a flat plate sensor formed of various layers of ceramic and electrolyte materials laminated and sintered together with electrical circuit and sensor traces placed between the layers in a known manner.
Because automotive exhaust constituent sensors are mounted to members of the vehicle exhaust flow system, the sensors must be durable and the sensors must be able to operate in a high temperature environment without being damaged by exposure to such high temperatures. The exhaust constituent sensors are typically installed in an exhaust pipe which is part of the motor vehicle's exhaust flow system and more specifically, the exhaust constituent responsive end of the sensor is disposed within an opening in the exhaust pipe so that exhaust gasses flow into the sensor and the level of the exhaust constituent to be sensed is communicated to a control system of the motor vehicle.
Typically, most exhaust constituent sensors have approximately the same length due to temperature requirements of a seal material and a terminal connection at one end of the sensor. More specifically, the length of the portion of the sensor which extends away from the exterior of the exhaust pipe is approximately the same for all conventional sensors to prevent excessive heat from traveling upward within the sensor to the seal material and the terminal connection. Consequently if the length of the sensor is too short, excessive heat is more likely to travel upward and contact the seal material and the terminal connection. Thus by extending the length of the sensor, the temperature of the heat is sufficiently reduced over time as it travels the length of the sensor and the seal material and the terminal connection are thermally protected and disposed away from the exhaust pipe, which reaches high temperatures during use of the motor vehicle. This is especially true for exhaust constituent sensors which are mounted in a spark ignition gasoline engine, close to the manifold outlet. The reasons for this is that most planar sensors are built with several air "pockets" preventing heat that is in the middle of the sensor from escaping out to the cooler outside diameter.